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Adsorption of chitosan on spin-coated cellulose films
A.L. Da Róz a,*, F.L. Leite c
, L.V. Pereiro a
, P.A.P. Nascente b
, V. Zucolotto a
, O.N. Oliveira Jr. a
, A.J.F. Carvalho c
a
Instituto de Física de São Carlos, Universidade de São Paulo (USP), São Carlos, Brazil
b
Universidade Federal de São Carlos, Campus São Carlos, Brazil
c
Universidade Federal de São Carlos, Campus de Sorocaba, Brazil
a r t i c l e i n f o
Article history:
Received 30 September 2009
Received in revised form 20 October 2009
Accepted 28 October 2009
Available online 5 November 2009
Keywords:
Cellulose
Chitosan
AFM
XPS
Thin films
Spin-coating
a b s t r a c t
This paper reports on the adsorption of an ultrathin chitosan layer on spin-coated films of cellulose,
where efficient attachment was induced by oxidizing cellulose which provided anionic sites for electro-
static interaction with the positively charged chitosan. Both the cellulose oxidation and the chitosan
adsorption were confirmed with Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron
spectroscopy (XPS) measurements. The molecular-level interaction between chitosan and cellulose
involved the NAH groups, as inferred from the disappearance caused by chitosan adsorption of the amide
band at 1667 cmÀ1
in the FTIR spectrum of cellulose. The XPS data confirmed a significant increase in the
atomic concentration of nitrogen groups, from 2.16% to 4.73% when chitosan was adsorbed on the oxi-
dized cellulose film, which also led to rougher films as illustrated by atomic force microscopy images.
One may now envisage applications in which the bactericide action of chitosan is combined with the bio-
compatibility of cellulose.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
The increasing use of cellulose in the pharmaceutical and paper-
making industries has demanded a refined understanding of its
physicochemical properties, processability and molecular-level
interactions (Kontturi, Thune, & Niemantsverdriet, 2003). Because
cellulose is insoluble in most organic and inorganic solvents, a de-
tailed investigation of interactions with other materials is not
straightforward. This limitation can be overcome by processing
cellulose in the form of ultrathin films (Eriksson, Notley, & Wåg-
berg, 2007; Falt, Wagberg, Vesterlind, & Larsson, 2004; Gunnars,
Wågberg, & Stuart, 2002; Holmberg et al., 1997; Kondo, Kasai, &
Brown, 2004; Kontturi, Tammelin, & Osterberg, 2006; Kontturi
et al., 2003; Notley, Eriksson, Wågberg, Beck, & Gray, 2006; Rad-
tchenko, Papastavrou, & Borkovec, 2005; Sczech & Riegler, 2006;
Yokota, Kitaoka, & Wariishi, 2007). Thin films were first produced
with cellulose derivatives, e.g. trimethylsiloxane cellulose (TMSC)
(Amim, Kosaka, & Petri, 2008; Holmberg et al., 1997; Kontturi
et al., 2003; Radtchenko et al., 2005; Tammelin, Saarinen, Sterberg,
& Laine, 2006), whose surface properties differed from those of cel-
lulose in natura. Another widely used strategy is the fabrication of
cellulose films via its solubilization in organic solvents such as N-
methylmorpholine-N-oxide (NMNO) (Eriksson et al., 2005, 2007;
Freudenberg et al., 2005; Gunnars et al., 2002; Notley et al.,
2006; Yokota et al., 2007), dimethylthexylsilyl chloride (TDMSCl)
(Kadla, Asfour, & Bar-Nir, 2007), aqueous NaOH/thiourea solutions
(Yan, Wang, & Chen, 2008) and lithium chloride (LiCl) in dimethyl-
acetamide (DMAc) (Eriksson et al., 2005, 2007; Kondo et al., 2004;
Notley et al., 2006; Radtchenko et al., 2005; Sczech & Riegler, 2006;
Wang, Chen, & Kim, 2007).
The possible control of molecular architectures and film proper-
ties afforded by methods such as the layer-by-layer (LbL) technique
(Decher, 1997; Leite et al., 2005) can be exploited in optimizing the
properties of cellulose. In this study, we covered spin-coated cellu-
lose films with a one-layer chitosan film adsorbed via electrostatic
interactions. The motivation for employing chitosan, a nontoxic and
antimicrobial copolymer consisting of b-(1,4)-2-acetamido-2-
deoxy-D-glucose and b-(1,4)-2-amino-2-deoxy-D-glucose units, lies
in the possible antimicrobial activity (Jeon, Park, & Kim, 2001; No,
Park, Lee, & Meyers, 2002). Existing methods to incorporate chito-
san into cellulose are based on the treatment of cellulose fibers with
chitosan, where the latter is anchored physically to the fibers. Here,
we improved chitosan adsorption by oxidizing cellulose, which
then had effective anchoring sites for chitosan. The investigation
of the anchoring process in a thin film instead of in naturally occur-
ring fibers showed to be more convenient and an interesting tool to
study cellulose interactions with other biomolecules.
2. Experimental
2.1. Materials
Glass slides coated with a gold layer were used as substrates.
Microcrystalline cellulose (type PH-101, AvicelÒ
– FMC – Belgium,
0144-8617/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carbpol.2009.10.062
* Corresponding author.
E-mail address: alessandra.roz@gmail.com (A.L. Da Róz).
Carbohydrate Polymers 80 (2010) 65–70
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol

3. Author's personal copy
with an average particle size of 50 lm) was used as raw material.
Dimethylacetamide (DMAc – Vetec – Brazil) was distilled from
CaH2 (Aldrich) and kept over activated 4 Å molecular sieves. Lith-
ium chloride (LiCl – Mallinckrodt – USA) was dried at 200 °C for
3 h and kept in a desiccator. Chitosan from shrimp was purchased
from Galena Chemistry, Brazil (120 Cps of viscosity and 85% de-
acetylation). Phosphoric acid (Synth Brazil), nitric acid (Quimis –
Brazil) and sodium nitrite (Hoecht) were used as oxidant agents.
Ninidryn (Mallinckrodt – USA), sodium acetate (Synth – Brazil)
and methylene blue dye were used as received.
2.2. Cellulose dissolution
Cellulose powder (Avicel) was dissolved in a solution of LiCl in
DMAc employing a procedure adapted from Ramos, Assaf, El Seoud,
and Frollini (2005). Briefly, 2 g of dry cellulose and 5 g of LiCl were
kept under constant stirring, and heated from room temperature to
110 °C at a rate of 3 °C/min to ensure water removal. After 1 h,
100 mL of DMAc were slowly added, and the system was heated
from 110 to 160 °C at 4 °C/min under vigorous stirring. After 1 h,
the system was slowly cooled to 36 °C at 1 °C/min, maintained
by stirring for 24 h.
2.3. Cellulose films preparation
Cellulose films were produced by the spin-coating technique.
The glass substrate was covered with the cellulose solutions and
spun at spin speeds of 1500 and 2500 rpm for 12 min. The slide
was dried at 90 °C under vacuum. After dried, the film was thor-
oughly washed in deionized water. Finally, the slides were dried
under a nitrogen flow and stored at 25 °C.
2.4. Oxidation of the thin cellulose film surface
The oxidation process of cellulose films was performed using a
solution of 0.0355 g of sodium nitrite in a mixture of 5 mL of
phosphoric and nitric acids (1/1 v/v) in deionized water (1=4 of acid
solution volume). The cellulose films were immediately immersed
in the solution for 15 s at 25 °C, followed by film washing in
deionized water and drying under a nitrogen flow.
2.5. Adsorption of chitosan
The cellulose samples were immersed in the chitosan solution
(1 wt.%) in acetic acid (1 wt.%) ($pH 2.7) for 1 min, followed by
washing in deionized water and drying at 115 °C, in a procedure
similar to those employed in the LbL technique (Leite et al., 2005).
2.6. Characterization
The oxidation of cellulose films and its interaction with chitosan
were monitored by measuring the infrared spectra with a FTIR
spectrometer BOMEM MB-102. Cellulose films were analyzed in
the reflection mode, whereas cellulose powder was investigated
using the transmission mode with KBr pellets (100:1). The oxida-
tion of the cellulose films was also monitored using UV–vis absorp-
tion spectra obtained with a HITACHI (U-2001) spectrophotometer.
X-ray diffraction patterns were acquired with a Rigaku X-ray
diffractometer with Cu K (k = 1.542 Å) radiation, submitted to
50 kV/100 mA, with scan speed of 2°/min (normal), grazing inci-
dence angle of 2° and exposed to radiation from 3° to 40° (2h).
The crystallinity index CrI was estimated by employing the
definition of Duchemin, Newman, and Staiger (2007), as CrI ¼
Hc
Ha
þ Hc
À Á
 100, where Hc is the height of the peak typically
located in the range 2h = 21–22° and Ha is the height measured
at 2h = 15°, which is related to the amorphous cellulose.
Fig. 1. FTIR spectra for the unmodified and oxidized cellulose.
Fig. 2. High resolution XPS spectra of the O1s peak for cellulose films: (a) non-
oxidized and (b) oxidized.
66 A.L. Da Róz et al. / Carbohydrate Polymers 80 (2010) 65–70

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X-ray photoelectron spectroscopy (XPS) analysis was performed
with a Kratos XSAM HS spectrometer, using monochromatized
Mg Ka radiation. The spectrometer was operated at 49 W, 7 kV,
and 7 mA, and the photon energy was 1253.6 eV. A pass energy
of 80 eV was used for high-resolution scans in a valence band anal-
ysis. The spot size was 15 Â 15 Â 1 mm. The binding energies for
all spectra were determined with respect to the C1s reference sig-
nal (CAH or CAC bands) at 285.0 eV. The Shirley background and
Gaussian/Lorentzian functions were used for fitting the peaks.
The surface features and roughness of spin-coated cellulose
films were evaluated with atomic force microscopy (AFM). The
AFM images were taken with a Nanoscope IIIa Multimode micro-
scope (Digital Instruments Inc.). Samples were scanned with a sil-
icon cantilever with spring constant of 20 N/m and tip radius of
10 nm (nominal values). All measurements were performed in
the tapping modeÒ
under ambient conditions. The AFM images
were analyzed using WSxM 4.0 software (Nanotec Electronica
S.L.) (Horcas et al., 2007).
3. Results and discussion
3.1. Formation and characterization of cellulose films
Fig. 1 shows the FTIR spectra of the cellulose spin-coated films,
with typical bands for cellulose at 3400–3450 cmÀ1
(hydroxyl
groups), 2880–2900 cmÀ1
(CAH stretching) and 1150–1085 cmÀ1
(ether bonding). No peak assigned to residual DMAc was observed
in the cellulose films, which indicates that the washing procedure
was efficient in removing the solvent. In many cases, anchoring
polymers are used to promote the adhesion of cellulose onto the
substrates (Falt et al., 2004; Gunnars et al., 2002; Notley et al.,
2006), but this was not necessary here, since cellulose films easily
attached to the glass surface. The presence of cellulose was con-
firmed with the XPS data, shown in Fig. 2a and Table 1. The observed
oxygen and CAO contribution at 286.7 eV, leading to C 59% and O
49%, are similar to the theoretical values for the C6H10O5 units (Bur-
rell, Butts, Derr, Genovese, & Perry, 2004). Only a small amount of
nitrogen was detected, possibly arising from residual solvent.
The X-ray diffractogram for the raw microcrystalline cellulose
powder (Avicel) displayed peaks at 2h = 10.37°, 19.96°, 21.90°
and 35.40°, as shown in Fig. 3a, which are typical of native crystal-
line cellulose I (Isogai, Usuda, Kat, Uryu, & Atalla, 1989). In contrast,
Fig. 3b shows that the spin-coated cellulose film obtained from
solution in LiCl/DMAc exhibited peaks at 2h = 11.80° and 21.00°
typical of cellulose III and analogous to the structure of regener-
ated cellulose (Isogai et al., 1989). The transformation of cellulose
I into cellulose III upon processing cellulose in the form of thin
films may be attributed to the treatment with liquid ammonia or
organic amines (Isogai et al., 1989; Wada, Nishiyama, & Langan,
2006). The broad peak at 2h = 21.0° with a width of approximately
9°, suggests that the two diffraction peaks from cellulose I combine
into a single broad peak in cellulose III (Duchemin et al., 2007). The
peak at 2h = 35.3° from cellulose I (Fig. 3a) was absent in the dif-
fractogram of cellulose III, which suggests disorder, consistent with
a semicrystalline matrix (Duchemin et al., 2007). Indeed, the dif-
fraction peaks for cellulose III in the films were broader, pointing
to a low crystallinity, with the crystallinity index, CrI, decreasing
from 83% for cellulose I to 67% for the film (cellulose III), in agree-
ment with Duchemin et al. (2007).
Fig. 4 shows the AFM images of gold substrates and cellulose
films spin-coated at 2500 rpm. The surface of gold in Fig 4a exhib-
ited a flat, smooth topography with root mean square (RMS)
roughness of %2.6 nm. For the cellulose film in Fig. 4b, the rough-
ness was ca. 13 nm owing to irregularities with a dense distribu-
tion of fibers. This roughness differs from those of cellulose films
in the literature (Notley et al., 2006; Radtchenko et al., 2005; Scz-
ech & Riegler, 2006), which were less rough. The differences may
be attributed to changes in the deposition method, solution prep-
aration, and film thickness.
Table 1
XPS ratio and semi-quantified atomic concentration for various samples.
Sample Concentration
(atomic%)
Ratio
C O N O2/
(C2 + C3)
C3/
C2
Cellulose thin film 58.79 38.84 1.22 0.78 0.25
Cellulose thin film coated with
chitosan
65.37 30.54 2.16 0.67 0.28
Oxidized cellulose thin film 54.91 40.60 1.24 0.90 0.26
Oxidized cellulose thin film coated
with chitosan
44.81 44.43 4.73 0.93 0.29
Fig. 3. X-ray diffraction pattern of (a) native cellulose and (b) cellulose thin film.
A.L. Da Róz et al. / Carbohydrate Polymers 80 (2010) 65–70 67

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3.2. Oxidation of cellulose films
The oxidation of cellulose films was carried out to increase
adhesion between cellulose and chitosan. Oxidation can produce
carboxylic acid groups that may interact electrostatically with
chitosan forming ion pairs. To verify whether oxidation was suc-
cessful, UV–vis analyses were carried out using methylene blue
as a colorant. The idea behind this approach is that a stronger
attachment of the cationic dye is achieved in the oxidized films. Ta-
ble 2 shows the absorbance at 660 nm for the dye, and non-modi-
fied and oxidized cellulose films. Oxidized cellulose exhibits a
stronger attachment to the dye (2Â) than for non-modified cellu-
lose, which points to the formation of anionic sites in the oxidized
films. This has important implications for the adsorption of
chitosan through electrostatic interactions, as will be discussed
later on.
Fig. 4. AFM images of (a) gold pattern (RMS = 2.6 nm, 2.5 Â 2.5 lm), (b) cellulose films (RMS = 13.0 nm, 2.5 Â 2.5 lm), (c) oxidized cellulose film (RMS = 11 nm, 5 Â 5 lm)
and (d) oxidized cellulose film covered with chitosan (RMS = 33 nm, 5 Â 5 lm).
Fig. 5. FTIR spectra showing anchoring of chitosan on the cellulose thin film: (a) cellulose thin film, (b) cellulose thin film coated with chitosan and (c) chitosan thin film.
68 A.L. Da Róz et al. / Carbohydrate Polymers 80 (2010) 65–70

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We also obtained high-resolution O1s XPS spectra for cellulose
and oxidized cellulose. Fig. 2 shows the spectra resolved into three
Gaussian/Lorentzian components for non-oxidized and oxidized
cellulose films, the most intense of which was centered at
533.0 eV, attributed to electrons from oxygen atoms that are
bonded to hydrogen atoms (OH) (Beamson & Briggs, 1992; Daniel-
ache et al., 2005; Matienzo & Winnacker, 2002). Another compo-
nent located at 534.5 eV is assigned to electrons from oxygen
atoms bonded to one carbon atom (AOA) (Shen, Anand, & Levicky,
2004), while the third component at 531.4 eV is assigned to car-
bonyl groups C@O (Beamson & Briggs, 1992) resulting from oxida-
tion. The presence of surface oxidation products and contaminants
also contributed to some extent to the O1s spectrum, with slight
excess of oxygen in most of the complexes (Table 1). Cellulose oxi-
dation was confirmed by the increase in the relative amount of car-
bonyl groups from 9% for cellulose to 13% for oxidized cellulose. In
addition, the oxidation (O incorporation) led to an increase in the
O/C ratio, from 0.78 to 0.90. The theoretical O/C ratio for pure cel-
lulose is 0.83, which should not be altered upon conversion of pri-
mary alcohol into aldehyde. If the oxidation proceeds with the
formation of a carboxyl group, the O/C ratio should change to 1,
as shown in Table 1 (DiFlavio et al., 2007). In summary, the XPS re-
sults confirmed the increase in the number of anionic sites in the
cellulose films upon oxidation.
Consistent with the XPS and UV–vis data, the FTIR spectrum for
an oxidized cellulose film in Fig. 1 displayed a shoulder at
1736 cmÀ1
assigned to carbonyl groups (El-Hendawy, 2006; Lo-
jewska, Miskowiec, Lojewski, & Proniewicz, 2005), which should
be only due to the difference between the spectra of oxidized
and non-oxidized cellulose (Aimin, Hongwei, Gang, Guohui, &
Wenzhi, 2005). The oxidation process induced a change in surface
morphology, as indicated in the AFM images of Fig. 4b and c. A pos-
sible explanation is that the acidic treatment induces deterioration
of the film surface, resulting in removal of material.
3.3. Adsorption of chitosan on cellulose
Fig. 5 shows the FTIR spectra for films of cellulose, chitosan and
cellulose coated with a layer of chitosan adsorbed via electrostatic
interactions, as in the LbL technique (Decher, 1997; Leite et al.,
2005). The FTIR spectrum for the neat chitosan film displays bands
at 3400–3450 cmÀ1
(hydroxyl groups stretching vibration), 3300
and 3200 cmÀ1
(symmetric and asymmetric NH stretching),
2874–2922 cmÀ1
(CAH stretching), 1667 cmÀ1
(C@O, amide I),
1591 cmÀ1
(NAH deformation), 1380 cmÀ1
(CH3 deformation),
1309 cmÀ1
(CAN stretching, amide III), 1079 cmÀ1
(amine CAN
stretching vibration) and 1150–1085 cmÀ1
(ether bonding) (Rosca,
Popa, Lisa, & Chitanu, 2005; Silverstein, Bassler, & Morril, 1994).
Differences between chitosan and cellulose spectra may be ob-
served at 1667 and 1591 cmÀ1
bands, attributed to C@O (amide
I) and NAH groups from chitosan, respectively. For the cellulose
film coated with a layer of chitosan, these two bands are combined
and shifted to 1617 cmÀ1
. The disappearance of the band from
amide I at 1667 cmÀ1
indicates that NAH groups from chitosan
interact with carbonyl groups, thus confirming the molecular
interaction between cellulose and chitosan (Lima, Lazarin, & Air-
oldi, 2005). This is a typical feature of films produced with the
LbL method owing to the intimate contact between adjacent layers
(Zucolotto et al., 2003).
The XPS data were also useful to study the chitosan adsorption.
The high-resolution N1s spectra for films of cellulose and oxidized
cellulose, both coated with a chitosan layer, are shown in Fig. 6.
The most intense component centered at 400.0 eV is due to elec-
trons from nitrogen atoms that are bonded to carbon atoms
(NAC) or non-protonated amine groups (Matienzo & Winnacker,
2002). A second peak at 401.9–402.4 eV is attributed to the oxi-
dized nitrogen or to a protonated nitrogen (Dambies, Guimon,
Yiacoumi, & Guibal, 2001; Matienzo & Winnacker, 2002). The
anchoring of very little chitosan is consistent with the small in-
crease in the atomic concentration of nitrogen groups, from 1.22
for cellulose to 1.24% for the same films after chitosan adsorption,
as indicated in Table 1. This shows that the untreated cellulose film
hardly anchors chitosan. A similar analysis showed the increase in
nitrogen concentration after oxidation of the cellulose film, from
2.16% to 4.73% (Table 1), a further evidence of the efficiency of
Fig. 6. High resolution XPS spectra of the N1s peak of (a) cellulose and (b) oxidized
cellulose, both with adsorbed chitosan.
Table 2
Absorbance values at 660 nm for the various samples investigated.
Sample Absorbance at 660 nm
Methylene blue 0.048
Cellulose thin film 0.038
Cellulose thin film + methylene blue 0.046
Oxidized cellulose thin film + methylene blue 0.110
A.L. Da Róz et al. / Carbohydrate Polymers 80 (2010) 65–70 69

7. Author's personal copy
the oxidation reaction in increasing the anchoring sites and conse-
quently chitosan adsorption.
The adsorption of chitosan on the spin-coated cellulose films
led to changes in surface morphology, as indicated in the tapping
mode AFM images of Fig. 4. Upon adsorption of chitosan the sur-
face texture became irregular, with a much larger roughness, i.e.
>30 nm in Fig. 4d in comparison to 11 nm for the oxidized cellulose
with no chitosan adsorption.
In summary, the results from AFM, XPS and FTIR demonstrated
a high compatibility between chitosan and oxidized cellulose,
probably due to interchain bonding, as reported for cellulose ace-
tate/chitosan films (Lima et al., 2005).
4. Conclusions
Spin-coated cellulose films could be obtained from a cellulose
solution in DMAc/LiCl, in which the crystalline structure was typ-
ical of cellulose III, i.e. with low crystallinity. The direct oxidation
of hydroxyl groups in such films, confirmed with FTIR spectroscopy
and XPS, provided anchoring sites for the adsorption of chitosan via
electrostatic interactions. The molecular-level interaction between
positively charged groups from chitosan and negatively charged
groups from the cellulose film surface was inferred from the disap-
pearance of the amide I and/or amide II band at 1667 cmÀ1
in the
FTIR spectrum of cellulose upon chitosan adsorption. This indi-
cated that NAH groups were involved in such molecular-level
interactions, which were ultimately responsible for the enhanced
adsorption of chitosan on the oxidized cellulose film. The adsorp-
tion of a chitosan layer on the cellulose film also induced morpho-
logical changes, with increased film roughness. The successful
adsorption of chitosan onto cellulose opens the way for a number
of applications, where the properties of biocompatibility and anti-
microbian or bactericide activities may be combined.
Acknowledgments
This work was supported by FAPESP, CNPq and CAPES (Brazil).
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